See biographies by G. Hicks (1936), R. O'Connor and D. L. Walker (1967), and B. Gelb (1973).
See biography by J. F. Roche (1957, repr. 1968).
See biography by S. W. McCall (1914, repr. 1972).
See studies by H. A. Kelly (3d ed. 1923), A. E. Truby (1943), and L. N. Wood (1943).
The reason for this is that the number of possible sub-groups of network participants is , where is the number of participants. This grows much more rapidly than either
so that even if the utility of groups available to be joined is very small on a peer-group basis, eventually the network effect of potential group membership can dominate the overall economics of the system.
However, this includes the (one) empty set, and N Singletons, which are not properly subgroups. So subsets remain, which is exponential, like .